Preheat the oven to 400°F. Peel and thinly slice the onion. Chop the zucchini into 1-inch pieces. Drain and rinse the black beans.
Add ¼ cup yogurt/sour cream to a blender. Halve the lime. Halve the avocado and remove the pit. Scoop out the avocado flesh and add it to the blender along with the cilantro (both leaves and stems), juice from the lime, garlic, half of the cumin, half of the pickled jalapeños, ½ cup water, and 1 tsp salt. Blend the green sauce until smooth.
Place a large skillet over medium-high heat with 2 tsp vegetable oil. Add the sliced onion and cook until softened and slightly browned about 3 to 5 minutes.
Add the zucchini, black beans, remaining cumin, and chili spice. Stir to combine and cook until hot, about 1 to 2 minutes. Season the enchilada filling with 1 tsp salt.
Spread ¼ cup of the green sauce on the bottom of an 8x8 baking dish. Cover the sauce with one layer of the corn tortillas, breaking them up as necessary to fit. Top with half the enchilada filling and drizzle with 2 tbsp green sauce.
Repeat with more tortillas, remaining enchilada filling, and 2 tbsp green sauce. To finish, add one more layer of tortillas and cover with another ¼ cup of the green sauce. Cover with foil and bake until heated through about 20 minutes. Thinly slice the radishes.
Remove the enchiladas from the oven and top with the remaining pickled jalapeños and sliced radishes. Divide black bean enchilada bake between plates and serve with any remaining green sauce.